DiffServ (differentiated services)
The DiffServ model for QoS was developed to differentiate IP traffic so that the traffic's relative priority could be determined on a per-hop basis.
By using DiffServ, traffic is classified based on priority. Then the traffic is forwarded using one of three IETF-defined per-hop behavior (PHB) mechanisms. This approach allows traffic with similar service characteristics to be passed with similar traffic guarantees across multiple networks, even if the multiple networks don't provide the same service the same way. This is an important feature because the Internet is really a network of multiple service provider networks.
DiffServ replaces the first bits in the ToS byte with a differentiated services code point (DSCP). The DSCP is then mapped to the PHB. This technique allows service providers to control how the DSCP codepoints are mapped to PHBs, and each time a packet enters a network domain it may be re-marked.
DiffServ, as described in RFC 2475, allows for five categories of service differentiation. They are: Relative Priority Marking; Service Marking; Label Switching; Integrated Services/Resource Reservation Protocol; and Static per-hop Classification.
QoS at the IP layer, Part 2, Network World Convergence Newsletter, 11/28/01.
Additional resources
IETF DiffServ working group
Diff-Serv provides quality of service
Network World Tech Update, 11/04/02.
DiffServ vs. MPLS
Compares the two approaches.
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